Solar cells are presently fabricated commercially by photolithographic processes. These processes often are complex and time consuming. The use of these processes has lead to high cell manufacturing costs which has limited the use of solar cells for terrestrial and space power applications.
During solar cell manufacture, solar cell device structures are built up by successively depositing and then patterning and selectively etching various combinations of metal, semiconductor, and insulator film layers on a suitable substrate. Solar cells typically employ many such film layers. Currently, conventional photolithographic processing methods are employed to pattern and etch the different film layer combinations during the manufacture of solar cells of all types.
During the patterning and etching of a single film layer combination, several steps are required to pattern and develop the photoresist used to mask the topmost film layer for subsequent etching in desired regions. Several other acid, reactive solution, or plasma etching steps are required to selectively remove this film layer from an underlying layer in unmasked regions.
For example, time consuming and costly steps in the fabrication of copper indium diselenide (CuInSe.sub.2), copper indium gallium diselenide (CuIn.sub.(1-x) Ga.sub.(x) Se.sub.2, where x can vary between 0 and 1) and amorphous silicon (a-Si) solar cells currently include the photolithographic processes that are separately used to pattern and selectively remove semiconductor film layers used in the cells from underlying metal electrode layers, and to pattern and selectively remove the metal electrode layers from underlying glass, polymeric, or other supporting substrates. For CuInSe.sub.2 and CuIn.sub.(1-x) Ga.sub.(x) Se.sub.2 solar cells, this most often involves the removal of combination semiconductor layers of CdZnS/CuInSe.sub.2 and ZnO/CdZnS/CuIn.sub.(1-x) Ga.sub.(x) Se.sub.2, respectively, from molybdenum (Mo) electrode layers and these Mo layers from glass. For a-Si cells, this often involves removal of an a-Si layer from a metal electrode layer [typically copper (Cu), aluminum (Al), molybdenum (Mo), or titanium (Ti)] and this metal layer from glass.
Complex photolithographic processing steps currently are also employed to produce etch mesas around the perimeters of gallium arsenide (GaAs) and gallium aluminum arsenide (Ga.sub.(1-x) Al.sub.(x) As, where x can vary between 0 and 1) solar cells during their manufacture as a means of reducing cell leakage currents. In addition, GaAs or Ga.sub.(1-x) Al.sub.(x) As solar cells used in space applications are generally shielded by a protective coverglass to minimize proton-induced damage that can degrade cell performance. Because cells are electrically connected to each other at their busbars, it is often cumbersome to extend a protective coverglass of the cell beyond the busbar region. The removal of all junction material in the region along the edge of the cell adjacent to, and outside of the busbar of a cell would eliminate the necessity to shield the cell in this region. Thus, methods capable of reliably producing etch mesas in order to remove junction material in this region are desired. The photolithographic processes available for producing these etch mesas in the GaAs and Ga.sub.(1-x) Al.sub.(x) As semiconductor layers for minimizing cell leakage currents and for minimizing cell radiation damage are sufficiently expensive that they can only be used in the fabrication of custom cells.
The fabrication of multiple layer solar cells requires the use of a number of processing steps. Many different production stations may be required to carry out these photoresist patterning and film layer selective etching steps. The need for these steps and associated production stations limits the production throughput of solar cells and adds to their fabrication costs. One method of patterning and removing a surface layer on a semiconductor substrate is the laser dry etching method wherein a laser excites a gaseous radical precursor compound to decompose it into at least a radical species which combines with and acts to volatilize constituent elements of the surface layer. For example, a krypton fluoride laser operating at 248 nm can excite gaseous carbon tetrachloride (CCl.sub.4) by photon absorption to create atomic chlorine which reacts with a copper surface forming cupric chloride and cuprous chloride which are desorbed from the surface by the incident laser light. This method has been disadvantageously only applied to a single constituent metal and is prone to create carbon containing deposits on the surface which limits the efficiency of the dry etching process. This method has limited use during the manufacture of the solar cells which contain complex surface layers, such as CuInSe.sub.2, CuIn.sub.(x) Ga.sub.(1-x) Se.sub.2, CdZnS, ZnO, GaAs, and Ga.sub.(x) Al.sub.(1-x) As. These and other disadvantages are solved or reduced using the present invention.